In general, a waveguide is a device, or a system of material boundaries, that is designed to confine and direct the propagation of electromagnetic waves, such as light or optical signals, along a length of the waveguide.
An electromagnetic wave is a vector field that has two primary and orthogonal polarization states or vector directions associated with its propagation. These polarization states are generally referred to as the Transverse Electric (TE) mode and Transverse Magnetic (TM) mode for optical waveguides. In the TM mode, the magnetic lines of flux are predominantly oriented parallel to the substrate on which the waveguide sits, while in the TE mode the electric lines of flux are predominantly oriented parallel to the substrate.
The performance of waveguides and other optical devices is often sensitive to the polarization state of the electromagnetic wave propagation. That is, certain optical devices require or prefer an inputted signal to have a certain polarization state for optimal operation. Therefore, it is sometimes necessary to convert or rotate the polarization state of a signal before it is inputted to a certain optical device.
While various devices exist for converting or rotating the polarization of optical signals, to Applicant's knowledge, these systems require additional and specialized materials, such for example magneto optic, gyrotropic, electrooptic, anisotropic or birefringent materials, which results in extra components and/or costs. Some devices also require externally applied electric fields or post-fabrication calibration. Further, some devices are wavelength dependent, introduce scattering loss, or are highly fabrication sensitive, thus limiting the scope of their application. Therefore, there is a need for an effective and efficient waveguide structure for rotating the polarization of an electromagnetic signal, which overcomes the above mentioned problems and limitations of prior art devices, and which is compatible and integratable with other optical circuit elements. It is to such a device, and methods for making and using the same, that the present invention is directed.